1. Field of the Invention
The invention relates in general to transport refrigeration systems of the type which hold a set point temperature by way of heating and cooling cycles, and more specifically to such systems which utilize hot compressor discharge gas for heating.
2. Description of the Prior Art
In the transportation of perishable products, it is recognized that it is necessary to provide refrigeration for the cargo space. It is also well known that it is necessary to periodically provide heat to remove the accumulation of frost or ice from the refrigeration system evaporator. Also, when transporting perishable products through areas having a cold climate, it is necessary to provide heat to the cargo space to prevent excessive cooling or freezing of the perishable products.
A well known method for providing heat for defrost and heating cycles is to divert hot compressor discharge gas from the normal refrigeration circuit directly to the evaporator to achieve the desired heating. When such a system switches from cooling to heating or defrost a sudden rise in compressor suction pressure occurs, due to the sudden dumping of liquid refrigerant that has condensed in the heretofore dormant hot gas lines. When using higher pressure refrigerant such as R-502 or R-22, this pressure rise can stall the engine which drives the compressor. In the past, an orifice was installed in the hot gas line to minimize the instantaneous pressure rise to prevent stalling. This orifice, however, restricted refrigerant flow even when the over load protection was no longer needed.